Improving electrochemical performance of NiO films by electrodeposition on foam nickel substrates

NiO films for lithium-ion batteries were deposited on copper plates and foam nickel substrates by electrodeposition and subsequent heat treatment at 300 °C. At a discharge/charge rate of 0.1 C, foam NiO films delivered reversible capacity larger than 650 mAh g⁻¹ and capacity retention over 93% after 50 cycles. NiO films deposited on foam nickel exhibited higher reversible capacity, better cyclability, as well as higher rate capability than those on copper plates. The unique three-dimensionally porous morphologies of foam NiO films were responsible for the better electrochemical performance, which provided not only high electrode/electrolyte contact area but also a good electronic conduction matrix. The present finding offers a new pathway for the large scale fabrication of high-energy-density electrodes for lithium-ion batteries.     

Study of copper foam-supported Sn thin film as a high-capacity anode for lithium-ion batteries

Three-dimensional porous Sn thin film electrodes were prepared by electroless deposition on copper foam, then its morphology and electrochemical property were studied by means of scanning electron microscope (SEM), X-ray diffraction (XRD), electrochemical cycling test and cyclic voltammetry (CV). The porous framework and micro-holes have shown a great structure advantage in restricting severe volume changes when the Sn thin film was employed as anode for lithium-ion battery. The film electrode of sample C with an initial capacity of 676 mAh g⁻¹ showed good cycle performance displayed by retaining a capacity of 313 mAh g⁻¹ after 100 cycles.     

Nanostructured Si/TiC composite anode for Li-ion batteries

Si/TiC nanocomposite anode was synthesized by a surface sol-gel method in combination with a following heat-treatment process. Through this process, nanosized Si was homogeneously distributed in a titanium carbide matrix. The electrochemically less active TiC working as a buffer matrix successfully prevented Si from cracking/crumbling during the charging/discharging process. The interspaces in the Si/TiC nanocomposite could offer convenient channels for Li ions to react with active Si. The Si/TiC composite exhibited a reversible charge/discharge capacity of about 1000 mAh g⁻¹ with average discharge capacity fading of 1.8 mAh g⁻¹ (0.18%) from 2nd to 100th cycle, indicating its excellent cyclability when used as anode materials for lithium-ion batteries.     

Engineering defect-enabled 3D porous MoS2/C architectures for high performance lithium-ion batteries

Designing defect-rich MoS₂/C architectures with three-dimensional (3D) porous frame effectively improve the electrochemical performance of lithium-ion batteries (LIBs) owing to the improved conductivity and decreased diffusion distance of Li⁺ ions for lithium storage. Herein, we report a reliable morphology engineering method combining with tunable defects to synthesize defect-rich MoS₂ nanosheets with a few layers entrapped carbon sheath, forming a 3D porous conductive network architecture. The defect-rich MoS₂ nanosheets with expanded interlayers can provide a shortened ion diffusion path, and realize the 3D Li⁺ diffusion with faster kinetics. A 3D conductive interconnected carbon network is able to improve interparticle conductivity, concurrently maintaining the structural integrity. Benefiting from these intriguing features, the as-prepared MoS₂/C architectures exhibit excellent electrochemical performance: a high reversible capacity of 1163 mAh g⁻¹ at a current density of 0.1 A g⁻¹ after 100 cycles and a high rate capability of 800 mAh g⁻¹ at 5 A g⁻¹. Defect content in MoS₂/C architectures can be obtained by changing H₂ concentration. Compared with the counterparts with few defects, the defect-rich MoS₂/C architectures show improved electrochemical stability with a superior cycle life, illustrating a highly reversible capacity of 751 mAh g⁻¹ at 0.5 A g⁻¹ after 500 cycles.     

Flower-like ZnO-NiO-C films with high reversible capacity and rate capability for lithium-ion batteries

Flower-like ZnO-NiO-C films with high reversible capacity and rate capability for lithium-ion batteries were fabricated through simple solution-immersion steps and subsequent heat treatment at moderate temperature. At a rate of 0.5 C, reversible capacity greater than 485 mAh g⁻¹ could be retained at the 50th cycle for ZnO-NiO-C films. More importantly, the films delivered reversible capacities of 380, 300, 230, and 180 mAh g⁻¹ at 1, 2, 3 and 4 C rates, respectively. The superior electrochemical properties of the ZnO-NiO-C films resulted from the advantages of flower-like architecture as well as the catalytic and conductive effects of the Ni phase produced in the first discharge process. Owing to easy fabrication and excellent electrochemical performance, these ZnO-NiO-C films will be promising anodes for lithium-ion batteries. The results of this study also offer possibilities of improving the lithium storage capacity of transition metal oxides by controlling both architecture and composition.     

On the activation and charge transfer kinetics of evaporated silicon electrode/electrolyte interfaces

Silicon is a promising negative electrode material candidate for lithium-ion thin-film batteries because of its very high theoretical storage capacity. Assuming full conversion of Si into Li₁₅Si₄, a theoretical capacity of 3579 mAh g⁻¹ or 8303 mAh cm⁻³ is expected. However, the interaction between silicon thin-film electrodes and various electrolytes (both liquid and solid) is, up until now, not well understood. The interface between the electrode and electrolyte plays a crucial role in the Li-(de)insertion reaction as here the actual charge transfer reaction takes places. To this end, some important issues on the activation of the electrode/electrolyte interface will be addressed in this paper. Moreover, new results on the temperature dependence of the charge transfer kinetics of evaporated silicon thin-film electrodes combined with four different liquid and solid electrolytes will be presented.     

Mesoporous polyaniline or polypyrrole/anatase TiO2 nanocomposite as anode materials for lithium-ion batteries

A functional composite as anode materials for lithium-ion batteries, which contains highly dispersed TiO₂ nanocrystals in polyaniline matrix and well-defined mesopores, is fabricated by employing a novel one-step approach. The as-prepared mesoporous polyaniline/anatase TiO₂ nanocomposite has a high specific surface area of 224 m² g⁻¹ and a predominant pore size of 3.6 nm. The electrochemical performance of the as-prepared composite as anode material is investigated by cyclic voltammograms and galvanostatic method. The results demonstrate that the polyaniline/anatase nanocomposite provides larger initial discharge capacity of 233 mAh g⁻¹ and good cycle stability at the high current density of 2000 mA g⁻¹. After 70th cycles, the discharge capacity is maintained at 140 mAh g⁻¹. The excellent electrochemical performance of the polyaniline/TiO₂ nanocomposite is mainly attributed to its special structure. Furthermore, it is accessible to extend the novel strategy to other polymer/TiO₂ composites, and the mesoporous polypyrrole/anatase TiO₂ is also successfully fabricated.     

An effective and simple way to synthesize LiFePO4/C composite

The cathode material is synthesized from FeC₂O₄·2H₂O and LiH₂PO₄ by a solid-state reaction using citric acid as a carbon source. The electric conductivity of the synthesized LiFePO₄ has been raised by eight orders of magnitude from 10⁻⁹ S cm⁻¹. The LiFePO₄/C composite shows a greatly enhanced rate performance and the cyclic stability at room temperature. It delivers an initial discharge capacity of 128 mAh g⁻¹ at 4C, which is retained as high as 92% after 1000 cycles. In addition, the tested low temperature character is attractive. At −20 °C, the composite exhibits a discharge capacity of 110 mAh g⁻¹ at 0.1C. The homogenous morphology, the porous surface, the small particles inside and the conductive carbon observed contribute much to obtain the favorable electrochemical performance.     

An optimized Ni doped LiFePO4/C nanocomposite with excellent rate performance

Both Ni doping and carbon coating are adopted to synthesize a nano-sized LiFePO₄ cathode material through a simple solid-state reaction. It is found that the Ni²⁺ has been successfully doped into LiFePO₄ without affecting the phospho-olivine structure from the XRD result. The images of SEM and TEM show that the size of particles is distributed in the range of 20-60 nm, and all the particles are coated with carbon completely. The results of XPS show the valence state of Fe and Ni in the LiFePO₄. The electronic conductivity of the material is as high as 2.1 × 10⁻¹ S cm⁻¹, which should be ascribed to the coefficient of the conductive carbon network and Ni doping. As a cathode material for lithium-ion batteries, the Ni doped LiFePO₄/C nanocomposite delivers a discharge capacity of 170 mAh g⁻¹ at 0.2 C, approaching the theoretical value. Moreover, the material shows excellent high-rate charge and discharge capability and long-term cyclability. At the high rates of 10 and 15 C, this material exhibits high capacities of 150 and 130 mAh g⁻¹, retaining 95% after 5500 cycles and 93% after 7200 cycles, respectively. Therefore, the as-prepared material is capable of such large-scale applications as electric vehicles and plug-in hybrid electric vehicles.     

Synthesis of LiFePO4/carbon composite from nano-FePO4 by a novel stearic acid assisted rheological phase method

LiFePO₄/carbon composite was synthesized at 600 °C for 4 h in an Ar atmosphere by a stearic acid assisted rheological phase method using amorphous nano-FePO₄ as the iron source. XRD, SEM and TEM observations show that the LiFePO₄/carbon composite has good crystallinity, ultrafine and well-dispersed particles of 60–150 nm size and in situ carbon coated on the surface of LiFePO₄ crystallites. The synthesized LiFePO₄/carbon composite shows a high discharge capacity of 160 mAh g⁻¹ and 155 mAh g⁻¹ at rates of 0.5 C and 1 C, respectively. Even at a high current density of 30 C, the material still presents a discharge capacity of 93 mAh g⁻¹ and exhibits an excellent cycling performance.     

Electrochemical properties of Si–Ge–Mo anode composite materials prepared by magnetron sputtering for lithium ion batteries

Si–Ge–Mo composites are prepared using an RF/DC magnetron sputtering method, and their potential use as anode materials for rechargeable lithium-ion batteries is investigated. The Si–Ge–Mo composite films present an amorphous structure. The reaction mechanism of the Si–Ge–Mo with Li is investigated by various analytical techniques. The fabricated Si_0.41Ge_0.34Mo_0.25 composite film shows excellent electrochemical properties, including a high energy density (1st charge: 1193 mAh g⁻¹), long cycleability (ca. 870 mAh g⁻¹ over 100 cycles), and good initial Coulombic efficiency (ca. 96%). Additionally, when coupled with a LiCoO₂ cathode, the Si_0.55Ge_0.22Mo_0.23 composite electrode used as an anode shows excellent cycleability with a high energy density. The excellent electrochemical properties demonstrated by the Si–Ge–Mo composite film electrode confirm its potential as an alternative anode material for lithium-ion batteries.     

Evaluation of ZnO nanorod arrays with dandelion-like morphology as negative electrodes for lithium-ion batteries

In this study, ZnO nanorod arrays have been evaluated for the negative electrodes of lithium-ion batteries. The ZnO nanorod arrays with dandelion-like morphology were directly grown on copper substrates by a hydrothermal synthesis process at 80 °C. X-ray diffraction, scanning electron microscopy, galvanostatic discharge-charge, and cyclic voltammetry were employed to characterize the structure and electrochemical property of the arrays. The array electrodes showed a stable capacity over 310 mAh g⁻¹ after 40 cycles, and good capacity retention as the anodes of lithium-ion batteries. It was believed that the unique dandelion-like binary-structure played an important role in the electrochemical performance of the array electrodes. The present finding opens the possibility to fabricate micro/nanometer hierarchical ZnO films that might be applied in lithium-ion batteries.     

Si–Al thin film anode material with superior cycle performance and rate capability for lithium ion batteries

To improve the electrochemical performance of Si thin film, we have investigated the effect of the addition of Al in the film. The Si–Al thin film were prepared by co-deposition from Si target embedded with Al rods on Cu foil. The atomic ratio of Al in the film is 18.69% estimated by energy-dispersive spectroscopy. The XRD and TEM analysis revealed that the Si–Al thin film was a complete amorphous structure. The electrochemical performance of the Si–Al thin film as anode material for lithium ion battery was investigated by the cyclic voltammetry and charge/discharge tests. The Si–Al thin film delivered a high reversible capacity of 2257.8 mAh g⁻¹ and an initial Coulombic efficiency of 85.9% at 0.05C rates. Compared with pure Si thin film with the same thickness, Si–Al thin film showed superior rate capability and cycle performance. And the Li⁺ diffusion coefficient of Si–Al thin film is much higher than that of Si thin film.     

Preparation and electrochemical performance studies on Cr-doped Li3V2(PO4)3 as cathode materials for lithium-ion batteries

Cr-doped Li₃V_2−xCr_x(PO₄)₃/C (x = 0, 0.05, 0.1, 0.2, 0.5, 1) compounds have been prepared using sol–gel method. The Rietveld refinement results indicate that single-phase Li₃V_2−xCr_x(PO₄)₃/C with monoclinic structure can be obtained. Although the initial specific capacity decreased with Cr content at a lower current rate, both cycle performance and rate capability have excited improvement with moderate Cr-doping content in Li₃V_2−xCr_x(PO₄)₃/C. Li₃V_1.9Cr_0.1(PO₄)₃/C compound presents an initial capacity of 171.4 mAh g⁻¹ and 78.6% capacity retention after 100 cycles at 0.2C rate. At 4C rate, the Li₃V_1.9Cr_0.1(PO₄)₃/C can give an initial capacity of 130.2 mAh g⁻¹ and 10.8% capacity loss after 100 cycles where the Li₃V₂(PO₄)₃/C presents the initial capacity of 127.4 mAh g⁻¹ and capacity loss of 14.9%. Enhanced rate and cyclic capability may be attributed to the optimizing particle size, carbon coating quality, and structural stability during the proper amount of Cr-doping (x = 0.1) in V sites.     

Nanosized Si/cellulose fiber/carbon composites as high capacity anodes for lithium-ion batteries: A galvanostatic and dilatometric study

Recently, we reported a simple method for obtaining nanosized silicon with promising electrochemical properties as an anode material for lithium-ion batteries; the method involves the formation of a composite electrode with cellulose fibers. It is demonstrated that the performance of these electrodes can be enhanced by the addition of conductive carbon black (CCB). This beneficial effect is not only a result of the improvement of electrical conductivity and inter-particle contacts, but also due to a reduction of the expansion and shrinkage undergone by the electrode when Li is inserted into Si or extracted from Li_xSi, as revealed by in situ electrochemical dilatometry measurements. The best results were obtained with a CCB of high surface area and porosity. The Si/cellulose fiber/carbon electrodes obtained delivered charge capacities as high as 1800 mAh g⁻¹ and exhibited good capacity retention on cycling. These electrodes also exhibited lower expansion/shrinkage compared to carbon-free electrodes on discharging and charging the cell, respectively.     

Electrochemical study of NiO nanoparticles electrode for application in rechargeable lithium-ion batteries

Nickel oxide nanoparticles were synthesized via a simple and inexpensive microwave-assisted synthesis method within a fast reaction time of less than 20 min. The calcination of as-prepared precursor at 600 °C produces single phase nickel oxide. The lattice structure and morphology of the sample were investigated by X-ray diffraction, field-emission scanning electron microscopy and field-emission transmission electron microscopy. The particle size range of the nickel oxide nanoparticles varied from 50 to 60 nm. Nickel oxide nanoparticles exhibited good electrochemical performances as an anode material for lithium-ion batteries. The prepared nickel oxide anode revealed a large initial discharge capacity of 1111.08 mAh g⁻¹ at 0.03 C rate and retained 80% of initial capacity (884.30 mAh g⁻¹) after 20 cycles. Furthermore, at elevated rate of 3.7 C, the charge capacity of the nickel oxide electrode was as high as 253.1 mAh g⁻¹, which was 35% greater than that of commercial bulk nickel oxide (188 mAh g⁻¹). The enhancement of the electrochemical performance was attributed to the high specific surface area, good electric contact among the particles and easier lithium ion diffusion.     

Strategy for improving the capacity and rate performance of LiNixCoyMn1−x−y electrode using Ti3C2Tx MXene additives

With the expanding range of applications for lithium-ion batteries, a great deal of research is being conducted to improve their capacity, stability, and charge/discharge rates. This study was performed to investigate the effects of MXene, which has a large surface area and metallic conductivity, as a conductive additive to the cathode, on electrochemical performance. The two-dimensional material MXene constructs a conductive network with zero-dimensional carbon black in plane-to-point mode to improve conductivity and contact area with active materials, thereby facilitating fast charge transfer. The conductive network reduces the internal resistance and polarization of the cathode and aids the diffusion of electrons. The electrode containing an appropriate amount of MXene showed improved rate performance, high discharge capacity (123.9 mAh g⁻¹ at 4 C), and excellent cycle stability at a high scan rate (125.8 mAh g⁻¹ at 2 C after 150 cycles) compared to pristine electrodes. Based on these results, Ti₃C₂T_x MXene is a promising conductive additive in the battery field.     

The role of particle size on the electrochemical properties at 25 and at 55 °C of the LiCr0.2Ni0.4Mn1.4O4 spinel as 5 V-cathode materials for lithium-ion batteries

The role of the particle size on the electrochemical properties at 25 and at 55 °C of the LiCr_0.2Ni_0.4Mn_1.4O₄ spinel synthesized by combustion method has been determined. Samples with different particle size were obtained by heating the raw spinel from 700 to 1100 °C, for 1 h in air. X-ray diffraction patterns revealed that all the prepared materials are single-phase spinels. The main effect of the thermal treatment is the remarkable increase of the particles size from 60 to 3000 nm as determined by transmission electron microscopy. The electrochemical properties were determined at high discharge currents (1C rate) in two-electrode Li-cells. At 25 and at 55 °C, in spite of the great differences in particle size, the discharge capacity drained by all samples is similar (Q_dch ≈ 135 mAh g⁻¹). Instead, the cycling performances strongly change with the particle size. The spinels with Φ > 500 nm show better cycling stability at 25 and at 55 °C than those with Φ < 500 nm. The samples heated at 1000 and 1100 °C, with high potential (E ≈ 4.7 V), elevate capacity (Q ≈ 135 mAh g⁻¹), and remarkable cycling performances (capacity retention after 250 cycles >96%) are very attractive materials as 5V-cathodes for high-energy Li-ion batteries.     

High-rate, high capacity ZrO2 coated Li[Li1/6Mn1/2Co1/6Ni1/6]O2 for lithium secondary batteries

Recently, there have been many reports on efforts to improve the rate capability and discharge capacity of lithium secondary batteries in order to facilitate their use for hybrid electric vehicles and electric power tools. In the present work, we present a ZrO₂-coated Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂. The bare Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂ shows a high initial discharge capacity of 224 mAh g⁻¹ at a 0.2 C rate. Owing to the stability of ZrO₂, it was possible to enhance the rate capability and cyclability. After 1 wt% ZrO₂ coating, the ZrO₂-coated Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂ showed a high discharge capacity of 115 mAh g⁻¹ after 50 cycles under a 6 C rate, whereas the bare Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂ showed a discharge capacity of only 40 mAh g⁻¹ and very poor cyclability under the same conditions. Based on results of XRD and EIS measurements, it was found that the ZrO₂ suppressed impedance growth at the interface between the electrodes and electrolyte and prevented collapse of the layered hexagonal structure.     

The compatibility of transition metal oxide/carbon composite anode and ionic liquid electrolyte for the lithium-ion battery

Three types of transition metal oxide/carbon composites including Fe₂O₃/C, NiO/C and CuO/Cu₂O/C synthesized via spray pyrolysis were used as anode for lithium ion battery application in conjunction with two types of ionic liquid: 1 M LiN(SO₂CF₃)₂ (LiTFSI) in 1-ethyl-3-methyl-imidazolium bis(fluorosulfonlyl)imide (EMI-FSI) or 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (Py13-FSI). From the electrochemical measurements, the composite electrodes using Py13-FSI as electrolyte show much better electrochemical performance than those using EMI-FSI as electrolyte in terms of reversibility. The Fe₂O₃/C composite shows the highest specific capacity and the best capacity retention (425 mAh g⁻¹) under a current density of 50 mA g⁻¹ for up to 50 cycles, as compared with the NiO/C and CuO/Cu₂O/C composites. The present research demonstrates that Py13-FSI could be used as an electrolyte for transition metal oxides in lithium-ion batteries.